Broad band antenna



y 9 195@ .1. T. BOLLJAHN BROAD BAND ANTENNA 2 Sheets-Sheet l Filed Sept 27 JOHN T BOLLJAHN y i956) J. T. BOLLJAHN 2,505,751

BROAD BAND ANTENNA Filed Sept. 27. 1946 2 Sheets-Sheet 2 gvwwvrob JOH N T. BOLLJAHN wow;

i 'atenteci May 2 UNITED STATES PATENT OFFICE BROAD BAND ANTENNA John T. Bolljahn, Richmond Calif. Application September 27, 194 6, Serial No. 699,649 9 Claims. (01. 250-33) (Granted under the act of March 3, 1883, as

amended April 30, 1928; '370 0. G. 757) This invention relates to antennas, and more particularly to a single non-directional broad band antenna which may be used where several antennas would otherwise be necessary and is especially well adapted for installation on aircraft.

Communication requirements in many different fields frequently necessitate transmitting and receiving with several sets of equipment over several difierent frequencies. Generally at least one antenna is provided for each equipment. This multiplicity of antennas is particularly undesirable in mobile and aircraft installations since all cannot be given the most advantageous location. A popular form of antenna for'this purpose is a rod-like quarter-wave dipole mounted vertically. In aircraft installations such antennas frequently fail from the effect of slipstream. They are easily broken and, because some aircraft fairly bristle. with such appendages, are frequently broken offby careless plane handlers as well as causing injury to careless people. 1

One solution might be the use of a single sleeve type antenna which employs about a quarter wave radiating element set in a grounded, coaxial section which extends from the ground plane a length of the order of an eighth wave length. The addition of the coaxial section serves to detune the antenna at its critical frequency and en-- ables it to operate over a broad band of frequen-.

cies. However, in order to establish the proper impedance between the coaxial section and the radiating element, and have the latter large enough to handle transmitter power, thecoaxiall section must be unfortunately large. This bulki-- ness is undesirable when made in aircraft installations because of its wind resistance. However,

if two pieces are cut, each from an opposite side of the coaxial section, a streamlined shape is ob-. v tained without losing the desired operating characteristics. This might be called an "open sleeve type antenna. The use of such antenna greatly reduces the number of antennas required thus providing in addition to its other advantages an economy in weight, and material.

It is therefore an object of this invention to provide a non-directional antenna with a broad frequency range which may be used where several antennas would otherwise be used.

It is a further object of this invention to provide a nondirectional, broad band antenna that is streamlined.

It is another object of this invention to pro-- vide a driven element partially enclosed by a pair It is still another object of this invention to Fig. 1 is a sectional view of one embodiment.

or this axis. I Fig. 2 is'a perspective view of the embodiment appearing in Fig. 1. Fig. 3 is a cross sectional view of the variant embodiment of this invention taken in a horizontal plane.

Fig. 4 is a perspective view of the same em bodiment appearing in Fig. 3. i

Fig. 5 is a diagrammatic view of a variant em-- bodiment of the invention showing the dimensions of the antenna elements therein. a Fig. 6 is a perspective view of the antenna shown in Fig. 5 as installed on the leading edgeof an aircraft's vertical fin.

invention taken along its longitudinal Fig. 7 is a perspective side view of the installation shown in Fig. 6.-

'Briefly, this invention utilizes a sleeve type antenna to provide nondirectional operation over a. broad band of frequencies. A novel type of open.

sleeve is-employed to provide the-advantages of-a closed sleeve without its bulk. The open sleeve.

construction affords versatility in design variat1on thereby providing a simple antenna easily adaptedto a multitude of uses and easily accoma modated by the installation facilities. 1

Referring now to Fig. 1 in detail, the antenna-l is shown 1n cross-section consisting, for instance,.

of three thin, fiat metal strips II), II, and I2. The

center strip i2 is the driven element and has an approximate length I9 of a quarter-Wave lengthas measured at the lower end of the frequency,

end for a distance I5A equal to its width. The.

two metal strips I0 and I I have a length I8 about half that of the driven element I2 and may be spaced equi-distant therefrom at a distance Il equalto about half the width I5 of said driven element. Thewidth l6 as again are their other:

dimensions, is chosen to minimize the Q of the open sleeve design. The driven element alone.

would tune sharply at the frequency for which it is a quarter wave length. The. addition of the. parasitic elements In and H has the effect of a grounded sleeve to detune the antenna and with this arrangement the antennawill operate suecessfully for any frequency between thatiior" which the driven element is a quarter wave length and that for which it is a halt wavelength. The antenna is equipped with a coaxial connector l3 for feeding a coaxialliner The outer conductor is connected to the parasitic elements via the-ground plane 20 and the center conductor [4- feeds: the driven element l2. The taper at the lower end of said driven element facilitates its; connection to said center conductor and mayalso serve to improve the impedance matching of the line and the antenna. The. vertical rows of holes in all three metal strips provide a means of mounting same to the ground'plane as will be further described belowin reference to Fig. 2.

In Fig. 2 "the embodiment of Fig. l is shown in perspective to demonstrate a means of assembling the various parts.v Two thin pieces, 2t and 22 cut from nonconducting material are fastened to each side of the three elementsrlll, H, and 12. said pieces of insulating material are held together and the elements held in placefbetween them 'by means of bolts each passing through both nonconducting sections and the appropriate; intervening element. For this purpose the elements are equipped with holes as shown in Fig. 1. The antenna structure so obtained may be affixed to the ground plane 2!) by four iangle pieces 23, 2({25 (one opposite'24 not shown) bolted to the ground plane and the antenna structure. The. lower bolts supportin the parasitic elements 'lil and H in the nonconducting sections 2| andj22 may also be used for attachment to these angle pieces; It will be noted that the resultant "structure is both streamlined and compact.

Figures3 and 4 illustrate a variant embodiment of the invention wherein the streamlining is'accomplished by the shape of the parasitic elements themselves. Fig. 3 is a crosssection of thisantenna in a vertical plane. The same driven element l2 and parasitic elements In and" H- as in Figs. 1 and 2 are used herebut in addition the parasitic elements I!) and H receive electrical support from a pair of curved metal sections 28 and 29 respectively. These curved metal sections join the outer edges of strips Ill and It at their respective centers from which line of intersection each curves toward the driven element l2. One section 28 may be given the smooth curve of a leading edge and the other 29 the more pointed shape of a trailing edge to improve the streamlining of the antenna. In this construction the two nonconducting sections 26 and 21 supporting the driven element are clamped between the curved portions of each parasitic element and its corresponding fiat strip. For a lighter construcv tion the flat strips l and II may be removed and 4 the curved sections 28 and 29 alone used as the parasitic elements.

The perspective view in Fig. 4 demonstrates a method of mounting the antenna structure to the ground plane 28. Angle brackets are used as described in reference to Fig. 2. It will be noted that the upper portion of the driven; element l2 has been tapered in this embodimentto lessen the eiiect of slipstream upon the antenna. For the same purpose a cap 30 of insulating material may be mounted on the tops of the parasitic elemerits, its periphery fitting flush therewith and sloping upward to the driven element I2. Said cap 30 is also useful as a moisture seal.

The structure shown in Figs. 5, 6, and 7 to which reference is now made, includes in part a driven element and two parasitic elements cut from metal i-oilr The relative dimension of these elements may be understood from the diagrammatic view in Fig. 5 in which the driven element 31 has a'maximum length 3| corresponding to-ayquarter wave length as determined-by theylower end of the: frequency" band to be covered. Saidgelement 31 has awidth'32v at its widest; point slightly less thanits' greatest length 3t. Its. lower end tapers anamount 36 as measured along itsv length equival'entito half its width i2. By adding a parasitic element on eachside. of the driven element the operable frequency'band oivthe antenna is ex-- tendedto the point where theidriven elementslength 31 approaches half a wave length'.., There parasitic elements 38 and 39; are much. smal er than the driven element and located equidistant therefrom about'its'basel The separation; 3510i said elements measures about one fourth the.

antenna "system of Fig. 5. In "these figures the piecesofmetal foil have been wrapped about the le'adi'ngjedg'e-of an aircraft's verticalfindf; For this'purpose it is essential that saidvertical fin be constructed of some nonconducting material to avoid auniversal' 'shortingof theantenna ele men't's andseri'ous interference with the ra'diati'on pattern. The metal strip 40, describe'd in Fig". 5 as; a ground'pla'ne, may be used as shown in Figs. 6 and 7 to facilitate the junction of the nonconductingjvertical mi 4'? to" themetal air-i craft fuselage 42 as'well'as to -provide a mounting means for the antenna. The bulk of the iuselage '42 provides a ground plarie-iotthe system. The antenna system may be f'ed by means of 'a coaxial cable 43 penetrating the fuselage 42 through fitting 48 having its 'centerconductor 44 joined to the tapered end of thelarge" drivenelement 3'I, and its outer conductor connected tothe ground plane 42. The free endor the cable 43 may be secured in proximity to the driven ele-f ment 31 by means of a bracket 4'5 clamping it to the metalstrip 40 atthe baseof the antenna. Adding this antenna system to an aircraft will eflect no change in the airs tream aboutthe= air craft and the system is versatile enough to replace most of the antennas otherwise required therefore removing the disturbance of the airstream brought about by the normal assortmentoiantennasr r I Although only limited and specific embodiments of the present invention have been shown and described, it may be modified without departing from the principles thereof and any such modifications are, therefore, deemed to be within the scope of the invention as defined by the appended claims.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

What is claimed is:

1. An antenna, comprising a driven element, a pair of parasitic elements disposed equal-distant from said driven element, a ground plane supporting said parasitic elements, nonconducting means extending from said driven element to each of said parasitic elements to form a substantially smooth surface therebetween and operative to support said driven element and streamline the antenna to the flow of air, and a connecting terminal for feeding said driven element whereby radiant energy may be transmitted and received nondirectionally over a broad band of frequencies.

2. An antenna, comprising a driven element having a taper at one end thereof, a pair of parasitic elements of a length less than said driven element and located equi-distant therefrom, a ground plane electrically connected to said parasitic elements, nonconducting means extending from said driven element to each of said parasitic elements to form a substantially smooth surface therebetween and operative to support said driven element and streamline the antenna to the flow of air, and a coaxial line feeding means having an inner and outer conductor, said feeding means arranged so that said outer conductor electrically connects to said ground plane and said inner conductor connects to said tapered end of said driven member.

3. An antenna, comprising a driven element cut from a fiat strip of metal and having a length several times its width, said element being tapered at one end thereof, a pair of parasitic elements also cut from fiat strips of metal and having a length less than said driven element and spaced equi-distant therefrom, nonconducting means extending from said driven element to each of said parasitic elements to form a substantially smooth surface therebetween and operative to support said driven element and streamline the antenna to the flow of air, a connecting means including a coaxial conductor having inner and outer conductors, said connecting means being arranged to feed the tapered end of said driven element from said inner conductor and said pair of parasitic elements from said outer conductor of said coaxial line, a ground plane supporting the combination and electrically connected. to said pair of parasitic elements and said outer conductor, whereby radiant energy may be transmitted and received nondirectionally over a broad band of frequencies.

4. An antenna, comprising a driven element cut from a flat strip of metal and having a length several times its width said element being tapered at one end thereof, a pair of parasitic elements also cut from fiat strips of metal and having a length less than said driven element, said parasitic elements being located co-planar with said driven element and on opposite sides thereof, a pair of thin nonconducting sections extending besaid sections being operative to support the driven element and streamline the antenna to the flow of air, a connecting means including a coaxial conductor having inner and outer conductors, said means being arranged to feed the tapered end of said driven element from said inner conductor and said pair of parasitic elements from said outer conductor of said coaxial line, a ground plane electrically connected to said pair of parasitic elements and said outer conductor, whereby radiant energy may be transmitted and received nondirectionally over a broad band of frequencies.

5. An antenna, comprising a driven element out from a flat strip of metal, and having a taper at one end thereof, a pair of parasitic elements also cut from strips of metal so as to have a length shorter than said driven element, said parasitic elements being located adjacent said driven element and bent along their width so as to resemble respectively the leading and trailing edges of a tear drop in cross-section placed about the driven element so that its longitudinal axis lies in the plane of said driven element, a connecting means including a coaxial line having inner and outer conductors, said means being adapted to feed said tapered end of the driven element from the inner conductor of said coaxial line and said pair of parasitic elements from the outer conductor, a ground plane supporting the combination and electrically connected to said pair of parasitic elements and said outer conductor, whereby radiant energy may be transmitted and received nondirectionally over a broad band of frequencies.

6. An antenna, comprising a driven element cut from a fiat strip of metal and having a length several times its width, said element being tapered sharply at one end and gradually at the other end, a pair of parasitic elements also cut from flat strips of metal so as to have a length shorter than said driven element, said parasitic elements being located equi-distant from said driven element and bent along their width so as to resemble respectively the leading and trailing edges of a tear drop in cross-section placed about the driven element so that its longitudinal axis lies in the plane of said driven element, a connecting means including a coaxial line having inner and outer conductors, said means being adapted to feed said sharply tapered end of the driven element from the inner conductor of said coaxial line and said pair of parasitics from the outer conductor, a ground plane supporting the combination and electrically connected to said pair of parasitic elements and said outer conductor, whereby radiant energy may be transmitted and received nondirectionally over a broad band of frequencies.

'7. An antenna, comprising a driven element cut from a flat strip of metal and having a taper at one end thereof, a pair of parasitic elements also cut from strips of metal so as to have a length shorter than said driven element, said parasitic elements being located equi-distant from said driven element and bent along their width so as to resemble respectively the leading and trailing edges of a tear drop in cross-section placed about the driven element so that its longitudinal axis lies in the plane of said driven element, a pair of thin nonconducting sections extending between the two parasitic elements operative to form an enclosure therewith and streamline the antenna to the flow of air, a connecting means including a coaxial line having inner and outer conductors, said means being adapted to feed said tapered end of the driven element from the inner conductor of tween the parasitic elements and enclosing same, said coaxial line and said pair of parasitic elements from the outer conductor, tagrounduplane mennsara iiaz' 'as'itie elments'being operative to 8 -9.An antenna, compiising a driven element having a "itapierat one fe'nii ther'edf,ia115afa;s1tic element- 6f 'a'filerfllgfih Ies's 'Jthan salid" driven element an'diocalte'd aja'ceritthereto, a xgroundifilaneelec- 'trically cdnne'c'tedto saidiparasitic lem'ent n'onconduetin'g'meansextending'from said dfiven'e'lement to said 'paras'iti'c 1em'ent"t0 form a slibst-antially smooth .suriace therebetween and operative'to support saiddr'iyen lemeritandystreamjline the antenna tothefi'ow of air, and a coaxial line "feeding'means having an 'inner' and outer conductor, said means arrangecLs'o that said outer conductor electrically connects (to said ground plane and said inner .condutor rconnets to said tapered end of said-driven element.

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' REFERENCES "CITED The fellowin g references are-e1 record in the fil-e =of this patent:

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